Today, ceramic paving, in particular ceramic tiles, is usually laid using the so-called thin-bed method, in which the ceramic paving is laid in a thin, adhesive layer of tile mortar. This method, which is satisfactory for interior applications, is problematic when ceramic paving is to be laid in an exterior area, because the effects of moisture and temperature on paving of this kind frequently result in the gradual destruction of the tiles or the base in which they are laid, and it becomes impossible to avoid the diminished reliability of this type of paving, with the result that costly repair work may be required.
The main problem encountered when laying ceramic paving in an exterior area is the unavoidable moisture stress on the ceramic paving, which is caused by rain water or by other moisture that is precipitated because of temperature variations in the environment. Moisture of this kind passes through the ceramic paving, and in particular through the joints, into the substratum, where it can accumulate. Because the thin-bed method is used, it is as good as unavoidable that cavities will form beneath tiles, and in time these cavities will be filled with the water that has penetrated as described above, thereby causing a permanent moisture stress, on the one hand on the ceramic paving and on the other hand on the substratum. Because of these unavoidable cavities, it is possible, in particular during the cold time of the year, that the water that accumulates within the cavities in the thin-bed mortar will freeze and expand, thereby causing the ceramic paving to separate. In the same way, the water that accumulates within the cavities can generate a great deal of steam pressure as a result of solar radiation on ceramic paving laid in an exterior area and, in the case of glazed tiles, for example, this can cause the tiles to shatter. The same thing can happen in the case of freezing temperatures, since the pores within the tiles fill with water as a result of the permanent moisture stress, and then expand in the event of frost. This results in similar shattering of the ceramic surface. Furthermore, the accumulated water can cause chalk to be released from the joint mortar and from the thin-bed mortar, and this can result in efflorescence from the joints. In addition, the tile adhesive in the hollow spaces beneath the ceramic paving, which is usually processed as plastic mortar, can become superficially dissolved and thereby lose its strength. In addition to the foregoing, it is difficult to control the crack behaviour of the ceramic paving and of the substratum because of the very different coefficients of expansion of the substratum, the thin-bed mortar, and the ceramic paving, which are brought about by the very high temperature differences between the high temperatures caused by solar radiation and the low temperatures caused by frost that occur in the exterior area.
For this reason, it has frequently been proposed that ceramic paving of this type that is laid in an exterior area can be laid in a more durable fashion in that water that penetrates unavoidably from the top surface of the ceramic paving is deliberately drained out of the substratum of the ceramic paving once again. The basic idea underlying all these solutions is to deliberately incorporate cavities in the substratum beneath the ceramic paving. These cavities are not enclosed but rather permit the moisture that has penetrated to drain off through appropriate channels and in the grade by itself. This prevents water from accumulating and also ventilates the unavoidable cavities beneath the ceramic paving. For this reason, the water that has penetrated can remain within the ceramic paving or in its substratum only briefly, and is thereby prevented from causing the damage described heretofore. Furthermore, substrata of this kind beneath ceramic paving also bring about deliberate decoupling between the ceramic paving and substratum since, for example, stress cracks or loading cracks can frequently occur because of the different rates of thermal expansion or elasticity between the ceramic paving and the substratum.
This type of configuration for a sealing and drainage system is described in DE 100 60 751 C1. In this configuration, what is proposed is a sealing and drainage system that has a plastic or bitumen layer underneath, above which are disposed a first non-woven layer that is of a first hydrophobic polymer; above this there is a drainage layer that is of a second hydrophobic polymer, and then, above this, a second non-woven layer that is of the first hydrophobic polymer. It is true that, within certain limits, this layered construction permits moisture that has penetrated to drain out of the substratum of a tile layer; however, the mechanical load-bearing capacity of a layered, construction of this kind is unsatisfactory since embedding the uppermost non-woven layer in the tile mortar does not permit adequate anchoring or reinforcing function. The drainage layer is in the form of a lattice-type layer, although no exact details for forming the lattice-type layer are provided.